W（郭威） Guo

Isospin effect in statistical sequential decay

Isospin effect of the statistical emission fragments from the equilibrated source is investigated in the frame of statistical binary decay implemented into the GEMINI code, isoscaling behavior is observed and the dependences of isoscaling parameters alpha and beta on emission fragment size, source size, source isospin asymmetry and excitation energies are studied. Results show that alpha and beta neither depends on light fragment size nor on source size. A good linear dependence of alpha and beta on the inverse of temperature T is manifested and the relationship of alpha=4C(sym)[(Z(s)/A(s))(1)(2)-(Z(s)/A(s))(2)(2)]/T and beta=4C(sym)[(N-s/A(s))(1)(2)-(N-s/A(s))(2)(2)]/T from different isospin asymmetry sources is satisfied. The symmetry energy coefficient C-sym extracted from simulation results is similar to 23 MeV which includes both the volume and surface term contributions, of which the surface effect seems to play a significant role in the symmetry energy.

Scaling of anisotropy flows in intermediate energy heavy ion collisions

Anisotropic flows ( v 1 , v 2 and v 4 ) of light nuclear clusters are studied by a nucleonic transport model in intermediate energy heavy ion collisions. The number-of-nucleon scalings of the directed flow ( v 1 ) and elliptic flow ( v 2 ) are demonstrated for light nuclear clusters. Moreover, the ratios of v 4 / v 2 2 of nuclear clusters show a constant value of 1/2 regardless of the transverse momentum. The above phenomena can be understood by the coalescence mechanism in nucleonic level and are worthy to be explored in experiments.

Roles of deformation and orientation in heavy-ion collisions induced by light deformed nuclei at intermediate energy

The reaction dynamics of axisymmetric deformed (24)Mg+(24)Mg collisions has been investigated systematically by an isospin-dependent quantum molecular dynamics model. It is found that different deformations and orientations result in apparently different properties of reaction dynamics. We reveal that some observables such as nuclear stopping power (R), multiplicity of fragments, and elliptic flow are very sensitive to the initial deformations and orientations. There exists an eccentricity scaling of elliptic flow in central body-body collisions with different deformations. In addition, the tip-tip and body-body configurations turn out to be two extreme cases in central reaction dynamical process.

Nucleon-nucleon momentum-correlation function as a probe of the density distribution of valence neutrons in neutron-rich nuclei

Proton-neutron, neutron-neutron, and proton-proton momentum-correlation functions (C-pn, C-nn, and C-pp) are systematically investigated for C-15 and other C-isotope-induced collisions at different entrance channel conditions within the framework of the isospin-dependent quantum-molecular-dynamics model complemented by the correlation after burner (CRAB) computation code. C-15 is a prime exotic nucleus candidate due to the weakly bound valence neutron coupling with closed-neutron-shell nucleus C-14. To study density dependence of the correlation function by removing the isospin effect, the initialized C-15 projectiles are sampled from two kinds of density distribution from the relativistic mean-field (RMF) model in which the valence neutron of C-15 is populated in both 1d5/2 and 2s1/2 states, respectively. The results show that the density distributions of the valence neutron significantly influence the nucleon-nucleon momentum-correlation function at large impact parameters and high incident energies. The extended density distribution of the valence neutron largely weakens the strength of the correlation function. The size of the emission source is extracted by fitting the correlation function by using the Gaussian source method. The emission source size as well as the size of the final-state phase space are larger for projectile samplings from more extended density distributions of the valence neutron, which corresponds to the 2s1/2 state in the RMF model. Therefore, the nucleon-nucleon momentum-correlation function can be considered as a potentially valuable tool to diagnose exotic nuclear structures, such as the skin and halo.

MEASUREMENT OF THE PROTON-PROTON CORRELATION FUNCTION FROM THE BREAK-UP OF (22)Mg AND (20)Ne

An experiment of 22Mg and 20Ne beams bombarding on a 12C target at an energy of 60~70 A MeV has been performed at the RIKEN projectile fragment separator (RIPS) in the RIKEN Ring Cyclotron Facility to study the two-proton correlated emission from 22Mg and 20Ne excited states. The two-protons momentum correlation functions have been obtained for 22Mg and 20Ne, respectively. The trajectories of the 22Mg decayed products (20Ne + p + p) were also measured to get the angular correlations between the two protons in Center of Mass of decaying system by relativistic-kinematics reconstruction. The results exhibit that 22Mg has the features of 2He cluster decay mechanism.

AZIMUTHAL ASYMMETRY AND CORRELATIONS OF HARD PHOTONS IN INTERMEDIATE ENERGY HEAVY ION COLLISIONS

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we investigated the directed flow and elliptic flow for proton-neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive directed flow and negative elliptic flow of directed photons are illustrated and they seem to be anti-correlated to the free protons flow. Also we calculated the two-photon correlation functions from which the information of photon source was extracted, and while two-photon azimuthal correlations are presented as a good method to extract the elliptic flow parameter v2 of direct hard photons.

Measurements of reaction cross section and fragment momentum distribution for N=10 proton-rich isotones

The longitudinal momentum (p//) distributions of fragments after one-proton removal and reaction cross sections (σR) for several N = 10 isotones at intermediate energy (~ 70A MeV) have been measured simultaneously at the RIken Projectile fragment Separator (RIPS). p// was measured using a direct time-of-flight (TOF) technique, while σR was determined using a transmission method. An enhanced σR is observed for 23Al comparing with its neighbors. The p// distribution for 22Mg fragments from 23Al one-proton removal reaction has been obtained for the first time. The experimental data are discussed within a Few Body Glauber (FBG) framework. Analysis of p// indicates a dominant d-wave component in the ground state of 23Al. This agrees with recent experimental results. We also suggest the possibility of an enlarged 22Mg core for proton-rich nucleus 23Al.